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Istituto Superiore di Sanità
EpiCentro - L'epidemiologia per la sanità pubblica
Istituto Superiore di Sanità - EpiCentro


National Surveillance - Bacterial Meningitis in Italy

Since 1994 the Local Health Agencies and the Hospital Administrations in Italy have reported hospitalized cases of suspected bacterial meningitis (1). The purpose of this special surveillance is to provide a more  timely description of the epidemiologic characteristics of bacterial meningitis in Italy, examine the efficacy and efficiency of chemoprophylaxis where indicated, and to characterize the circulating bacterial strains collected by the Istituto Superiore di Sanità (ISS).

 

The number of cases of bacterial meningitis notified every year has been increasing steadily, from 620 cases in 1994 to 1029 in 1999, reflecting improvements in the completeness of surveillance. The most frequently identified pathogen among the cases of meningitis notified between 1994 and 1999 was Steptococcus pneumoniae (32% of cases), followed by Niesseria meningitidis (29%) and Hemophilus influenzae (H. influenzae) type b (18%).  A consistent proportion of the cases (approximately 20%) are notified as being of probable bacteriologic etiology, but the causative agent is not identifiable. This finding is not unexpected since many patients are already on antibiotics at the time of admission, thereby reducing the likelihood of isolating the causative organism.

 

Figure 1 shows the number of notifications for the three most common etiologic agents and for cases with unknown etiology. There has been an increase in the notifications for pneumococcus and meningococcus, especially in the number of cases of the latter during 1999, while the number of cases of H. influenzae have decreased. The decline in the number of cases caused by this pathogen also has been observed in a special H. influenzae surveillance system that was started in 1997 in 8 of the country’s 22 regions. At least part of the decrease is attributable to increases in the use of polyvalent infant vaccines containing a H. influenzae type b component.

Overall, the incidence of meningococcal meningitis in Italy in 1999 was 4.7 cases per million residents, one of the lowest rates reported in Europe. Seventy percent of the cases for which a strain had been sent to the ISS were due to serogroup B, and 19% to serogroup C.

 

The annual incidence of pneumococcal meningitis was 5.2 per million residents.  The most frequently represented serogroups were 14 and 23. Approximately 96% of the identified serogroups are contained in the polysaccharide vaccines (2).

 

The annual incidence of H. influenzae meningitis was 1.3 per million residents.  In 1999, among the 78 cases for whom typing was available, 98% were Type B. The incidence in Italy is higher than observed in other European countries (3). This higher incidence is attributable to lower use of vaccine in Italy, which only recently has begun to increase.

 

The distribution of the three major pathogens varies considerably by age group.  Most (85%) of the cases of H. influenzae meningitis were reported among children 0-4 years of age; while the age groups 0-4 years of age and 15-19 years of age accounted for 31% and 15% of the cases, respectively. By contrast, those over 65 accounted for 29% of the pneumococcal meningitis cases.

 

There were major geographic differences in the incidence of the three main types of meningitis, with a characteristic north-south gradient (Table 1). Small numbers, especially in regions with limited populations, render some of the rates unstable. Nonetheless, it is not clear why there are so few cases notified from some of the populous regions such as Puglia and Calabria, and why rates are so high in the autonomous provinces of Bolzano and Trento.

Caution is required in interpreting bacterial meningitis notifications and their geographic differences since it is not possible to evaluate regional differences in completeness of coverage of the surveillance system. However, these data nonetheless represent a unique source of ongoing information in time.

 

The occurrence of a case of meningitis in the community is always a source of considerable alarm, both because of the seriousness of the illness and the possible risk of an epidemic. In reality, outbreaks in Italy are rare, and, for example, in only 2% of the cases of meningococcal meningitis are associations identified between cases. Nonetheless, the fear of the population and the pressure of public opinion often result in unjustified interventions on the part of health care workers, such as the closure of schools, the search for carriers, or extensive antibiotic prophylaxis administered to persons who had no contact with the case.

 

References

1. Circolare del Ministero della Sanità, D.G.S.I.P., del 29 Dicembre 1993.

2. Pantosti A, D’Ambrosio F, Tarasi A, et al. CID 2000; 31: 1373-9.

3. Ramsay M., Final Report from the Project "An evaluation of Haemophilus influenzae type b vaccination and description of risk factors for Hib vaccine failure in Europe, 1996-98. PHLS, CDSC, Colindale, London, UK.

Stefania Salmaso Laboratorio di Epidemiologia e Biostatistica Istituto Superiore di Sanità

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